Electrophotography roller

ABSTRACT

An electrophotography roller incorporated in an image creating device by the electrophotography comprising a conductive shaft disposed along the center axis, a conductive elastic layer around the shaft, a surface layer on the conductive elastic layer formed concentrically. The JIS A hardness of the conductive elastic layer is 30° or less. The shear modulus of the conductive elastic layer measured in viscoelasticity under the condition of 20° C., 60% PH and 0.1 Hz is 4 10 5  Pa or more. The width of contact of the roller with another member is sufficiently ensured even under a low pressing pressure. The compression residual strain is small even after the roller is pressed against another member for a long time. If the roller is used as a development roller, a sharp image with less density unevenness due to the residual strain is created.

This application is a nationalization of PCT application PCT/JP00/08797filed Dec. 13, 2000. This application claims priority from the PCTapplication and Japan Application Serial No. H11(1999)-357445 filed Dec.16, 1999.

TECHNICAL FIELD

This invention relates to a roller that is part of an imaging devicethat features electrophotography, such as a copy machine, printer, or afax machine.

BACKGROUND ART

With an electrophotographic imaging device, various rollers are disposedin the vicinity of an electrostatic latent image support, such as acharging roller for uniformly supplying an electric charge to thiselectrostatic latent image support, a developing roller for supplyingtoner to the electrostatic latent image support, and a transfer rollerfor transferring the toner image from the surface of the electrostaticlatent image support onto recording paper.

FIG. 1 is a diagram illustrating an example of such anelectrophotographic imaging device. A charging roller 20 rotates withits surface in contact with a photosensitive element 21 (anelectrostatic latent image support), and uniformly supplies an electriccharge to the surface of the photosensitive element 21. Aphotoconductive insulator layer is formed on the surface of thephotosensitive element 21, and a conductor layer is formed under thisphotoconductive insulator layer. An electrostatic latent image is formedwhen light 22 including image information strikes the surface of thephotosensitive element 21. A developer 23 makes this electrostaticlatent image visible.

The developer 23 comprises a toner container 25 in which toner 24 isstored, a regulator blade 26 provided to this toner container 25, adeveloping roller 27, a supply roller 28 for securely supporting thetoner 24 on the surface of this developing roller 27, etc. Thedeveloping roller 27 comprises a conductive elastic layer concentricallyprovided around a conductive shaft made of SUS, an aluminum alloy, orthe like, and in some cases this conductive elastic layer is coveredwith a protective layer (surface layer). Voltage is applied between thisconductive shaft and the surface of the developing roller. The toner 24inside the toner container 25 consists of a non-magnetic toner, is heldon the surface of the developing roller 27, and is charged bycontact/friction when made into a thin toner layer by the regulatorblade 26. When the surface of the developing roller 27 is brought intocontact with the surface of the photosensitive element 21, the thintoner layer adheres to the electrostatic latent image on thephotosensitive element 21 surface, forming a toner image on the surfaceof the photosensitive element 21. This toner image is electrostaticallyadsorbed to the surface of recording paper 30 by a transfer roller 29,producing a transfer image on the recording paper 30. This transferimage is fixed to the recording paper 30 by a heating roller 31 and apressing roller 32. A blade or other cleaner 33 is provided on thedownstream side of the transfer roller 29 in order to remove any tonerpowder that is not transferred and remains on the surface of thephotosensitive element 21. A brush or roller is sometimes used insteadof this blade.

Of the various rollers used in the above-mentioned electrophotographyimaging device, the charging roller, developing roller, and transferroller all have the same basic structure. Specifically, these rollersare configured such that a conductive elastic layer is formed around aconductive shaft, and in some cases a protective layer (surface layer)covers this conductive elastic layer. This conductive elastic layerneeds to allow suitable elastic deformation. For instance, in the caseof a charging roller, for the charge on its surface to be supplied tothe photosensitive element, there needs to be a certain contact width inthe peripheral direction between the charging roller and thephotosensitive element. A low-hardness roller is used for the chargingroller in order to ensure the proper contact width. In the case of adeveloping roller, the correct contact width in the peripheral directionis required between the developing roller and the photosensitive elementin order for the toner held on the surface of the developing roller toadhere efficiently to the photosensitive element. Technology has beenintroduced in which a low-hardness developing roller is used in order toreduce the stress on the toner and ensure the proper contact width. Inthe case of a transfer roller, the required reproduced image can beobtained by electrostatically transferring the toner image to arecording medium (such as recording paper), either directly or via anintermediate transfer element, but ensuring the appropriate contactwidth in the peripheral direction is important in order to raise thetransfer efficiency, so a low-hardness roller is again used.

To achieve the desired deformation, NBR (nitrile butadiene rubber),urethane, EPDM (ethylene propylene rubber), silicone, or another suchrubber is frequently used as the material for the conductive elasticlayer of the various rollers discussed above. The use of low-hardnessrollers has been increasing in an effort to improve the quality ofreproduced images and lessen toner stress. This low hardness can beachieved by foaming the rubber layer to reduce its hardness, or bylowering the crosslink density, but a problem with such rollers is thatwhen a printer or copy machine is started up after not being used for anextended period, strain remains in the rollers, which can lead to voids,uneven density, and so forth in the toner image or reproduced image.This happens because the rollers are fixed for an extended period in astate in which they are pressed against the photosensitive element,intermediate transfer element, or other members, so residual compressionstrain remains.

The inventors conducted diligent research in light of these problems,and as a result perfected a roller that has low enough hardness toensure the proper contact width in the peripheral direction between theroller and other members even at a low pressing force, and that haslittle residual compression strain even when left compressed in a statein which it is pressed against another member for an extended period.

DISCLOSURE OF THE INVENTION

The inventors conducted diligent research aimed at solving the aboveproblems, and as a result arrived at the present invention upon turningtheir attention to the hardness and elastic modulus of the conductiveelastic layer of a roller. Specifically, the inventors discovered that,with a roller in which a conductive shaft is disposed along a centeraxis, a conductive elastic layer is provided concentrically around saidconductive shaft, and a surface layer is formed concentrically over saidconductive elastic layer, if the conductive elastic layer has a JIS Ahardness of no more than 30°, and the shear modulus of the conductiveelastic layer, measured as the viscoelasticity at 0.1 Hz in anenvironment of 20° C. and 60% RH, is at least 4×10⁵ Pa, then the propercontact width in the peripheral direction can be ensured between theroller and other members even at a low pressing force, and there will belittle residual compression strain in the roller even when it has beencompressed and fixed in a state of being pressed against another memberfor an extended period.

The roller of the present invention is preferably designed such that theroller resistance prior to the formation of the surface layer, that is,at the stage when only the conductive elastic layer has been formedaround the conductive shaft, is at least 10³ Ωcm, and the rollerresistance after the formation of the surface layer is 10⁴ to 10¹⁰ Ωcm.The reason for this is that the usable range of resistance for thedeveloping roller, charging roller, and transfer roller built into anelectrophotographic imaging device is the above-mentioned 10⁴ to 10¹⁰Ωcm. The term “roller resistance” as used in the present invention isthe value measured by applying a DC voltage of 100 V between theconductive shaft and a metal plate when a load of 500 g is applied toeach end of the shaft in the metal plate direction.

It is particularly favorable for the conductive elastic layer to be areaction product of a curable composition whose main components are (A)a polymer that contains at least one alkenyl group in its molecule, andin which the repeating units that make up the main chain consist mainlyof oxyalkylene units, and/or a polymer composed of saturatedhydrocarbon-based units, (B) a curing agent that contains at least twohydrosilyl groups in its molecule, (C) a hydrosilylation catalyst, and(D) a conductivity imparter.

It is preferable for the main component of the surface layer to beeither a single resin selected from the group consisting of urethaneresins, acrylic resins, silicone resins, and fluororesins, or a blend ofthese resins.

Furthermore, it is preferable for the material of which the surfacelayer is made to have an elongation of at least 300%. An elongationbetween 300% and 600% is particularly good, and a range of 400% to 600%is even better. The term “elongation” as used in the present inventionis the elongation at break as measured according to JIS K 6251.

The electrophotography roller pertaining to the present invention can beused as a charging roller or transfer roller built into anelectrophotographic imaging device, a developing roller built into adeveloping device that supplies toner to an electrostatic latent imagesupport, or the like.

Various working examples that are representative of the rollerpertaining to the present invention will now be described throughreference to the drawings. FIG. 2 is a diagram schematicallyillustrating a developing roller 1, which is an example of theelectrophotography roller pertaining to the present invention, and itssurrounding structure. The developing roller 1 pertaining to the presentinvention comprises a conductive elastic layer 3 concentrically providedaround a conductive shaft 2 having a diameter of about 1 mm to 25 mm andmade of SUS, an aluminum alloy, conductive resin or the like, and theouter peripheral surface of this conductive elastic layer 3 is coveredwith a surface layer 4 in a specific thickness between 10 and 50 μm. Theconductive elastic layer 3 has a JIS A hardness of no more than 30°, andits shear modulus, measured as the viscoelasticity at 0.1 Hz in anenvironment of 20° C. and 60% RH, is at least 4×10⁵ Pa. The surfacelayer 4 preferably has an elongation at break (measured according to JISK 6251) of at least 300%, and it is even better if the elongation of thesurface layer 4 is at least 400%. A resistance adjusting layer foradjusting the electrical resistance of the developing roller 1 may insome cases be provided between the conductive elastic layer 3 and thesurface layer 4, and one or more primer layers may also be included forincreasing the adhesion between the conductive elastic layer 3 and thesurface layer 4. The surface layer 4 can be formed by dipping, spraying,roll coating, brush coating, or another such method as dictated by theviscosity of the resin component that makes up the surface layer 4, forexample, but there are no particular restrictions on how this surfacelayer 4 is formed in the present invention.

Non-magnetic toner 6 stored in a toner container 5 is supported on thesurface of the developing roller 1 and made into a toner thin film 8 ofa specific thickness by a regulator blade 7, after which the toner thinfilm 8, which has been friction charged in the course of being made intothe toner thin film 8 by this regulator blade 7, adheres to anelectrostatic latent image on the surface of a photosensitive element 9.The non-magnetic toner 6 is efficiently supplied to the developingroller 1 here by a supply roller 10. The supply roller 10 can be in theform of a sponge, such as a conductive foam composed of polyurethane orthe like, or it can be a conductor such as a metal pipe composed ofaluminum or the like. The non-magnetic toner 6 can comprise a coloringpigment covered with a styrene-acrylic-based or polyester-basedthermoplastic resin or the like, and has a particle diameter of about 6to 10 μm, for example.

In this example, DC voltage is applied to the developing roller 1 andthe supply roller 10. If the toner 6 is negatively charged, it ispreferable to apply a DC voltage of −150 to −350 V to the developingroller 1 and −200 to −600 V to the supply roller 10. A DC voltage of−150 to −600 V can also be applied to the regulator blade 7 in order tocontrol the charge of the toner 6. If the toner 6 is positively charged,then the DC voltages applied to the developing roller 1, the supplyroller 10, and the regulator blade 7 will be of the opposite sign, butof the same absolute values as above. AC voltage can also be superposedover the DC voltage.

It is preferable for the conductive elastic layer 3 to have a rollerresistance of at least 10⁴ Ω before being covered with the surface layer4. This is because when a DC voltage is applied to the developing roller1, fluctuation in roller resistance can be kept low in the event thatthere is any coating unevenness of the surface layer 4. Furthermore, theroller resistance after being covered by the surface layer 4 should be10⁴ to 10¹⁰ Ω, and preferably between 10⁵ and 10⁹ Ω, so that thephotosensitive element 9 will not be damaged and a good image will beobtained.

During developing, the surface of the developing roller 1 rotatesaxially while being pressed against the surface of the photosensitiveelement 9 at a specific contact width in the peripheral direction(hereinafter referred to as the nip width). The nip width must be about0.5 to 2.0 mm. Thus, during developing, the surface of the developingroller 1 rotates axially while its pressing location on thephotosensitive element 9 varies in the peripheral direction. The resultof using the developing roller 1 pertaining to the present invention,that is, a roller comprising a conductive elastic layer concentricallyprovided around the conductive shaft 2, and the surface layer 4concentrically provided around over this conductive elastic layer 3,wherein the conductive elastic layer 3 has a JIS A hardness of no morethan 30°, and the shear modulus of the conductive elastic layer,measured as the viscoelasticity at 0.1 Hz in an environment of 20° C.and 60% RH, is at least 4×10⁵ Pa, is that the proper nip width at thephotosensitive element 9 can be ensured at a low pressing force, andthere is less residual strain in the conductive elastic layer 3 afterthe layer 3 has been pressed against the photosensitive element 9, theregulator blade 7, or the like for an extended period, which makes itpossible to obtain a sharp image with no voids, toner densityunevenness, or the like immediately after the developing device isstarted up. When a reduction in toner stress is taken into account, itis preferable for the JIS A hardness of the conductive elastic layer 3to be no more than 25°. Also, in terms of the level of compressionstrain, it is preferable for the shear modulus of the conductive elasticlayer 3 to be at least 4.5×10⁵ Pa.

The structure of the conductive elastic layer of the roller pertainingto the present invention will now be described in detail.

Urethane rubber, silicone rubber, or other such liquid rubber can beused as the material for the conductive elastic layer with a JIS Ahardness of no more than 300 and a shear modulus of at least 4×10⁵ Pameasured as the viscoelasticity at 0.1 Hz in an environment of 20° C.and 60% RH, but a crosslinked rubber produced by the hydrosilylation ofa liquid rubber (discussed below) is particularly favorable because ithas a flexible structure. Specifically, it is preferable to use areaction product of a curable composition whose main components are (A)a polymer that contains at least one alkenyl group in its molecule, andin which the repeating units that make up the main chain consist mainlyof oxyalkylene units, and/or a polymer composed of saturatedhydrocarbon-based units, (B) a curing agent that contains at least twohydrosilyl groups in its molecule, (C) a hydrosilylation catalyst, and(D) a conductivity imparter. If the polymer of component A includesoxyalkylene groups, the uncured composition will be easier to handlebecause of its lower viscosity, and it is favorable for the polymer ofcomponent A to include saturated hydrocarbon units because theconductive elastic layer after curing will have a lower moistureabsorption rate, so there will be less change in the roller resistancein high humidity environments.

The polymer of component A in this curable composition cures through ahydrosilylation reaction with component B, and has at least one alkenylgroup in its molecule, and therefore becomes macromolecular and cureswhen the hydrosilylation reaction occurs. The number of alkenyl groupsincluded in component A must be at least one from the standpoint of thehydrosilylation reaction with component B, but from the standpoint ofrubber elasticity, it is preferable for two alkenyl groups to be presentat the ends of the molecule in the case of a straight chain molecule,and for two or more alkenyl groups to be present at the molecular endsin the case of a branched molecule.

The main repeating units that make up the main chain of component A areoxyalkylene units and/or saturated hydrocarbon units.

When component A is a polymer in which the main repeating units thatmake up the main chain consist of oxyalkylene units, only a small amountof conductivity imparter need be added because the volumetricresistivity of the cured product will be from 10⁸ to 10⁹ Ωcm. From thestandpoint of the cured product having low hardness, the above-mentionedoxyalkylene-based polymer in which the repeating units are oxyalkyleneunits is preferable, and particularly an oxypropylene-based polymer inwhich the repeating units are oxypropylene units.

The term “oxyalkylene-based polymer” as used here means a polymer inwhich at least 30%, and preferably at least 50%, of the units that makeup the main chain consist of oxyalkylene units. Examples of units otherthan oxyalkylene units that may be contained include compounds havingtwo or more active hydrogens, such as ethylene glycol, bisphenolcompounds, glycerol, trimethylolpropane, pentaerythritol, and other suchunits. In the case of an oxypropylene-based polymer, this may also be acopolymer with units consisting of ethylene oxide, butylene oxide, orthe like (including graft copolymers).

From the standpoint of striking a good balance between reactivity andreduction of the hardness of the cured product, it is preferable for themolecular weight of the oxyalkylene-based polymer of component A to befrom 500 to 50,000, and even more preferably 1000 to 40,000, as thenumber average molecular weight Mn. A number average molecular weight Mnof 5000 or higher is especially good, and a range of 5000 to 40,000 isbest. If the number average molecular weight Mn of the oxyalkylene-basedpolymer of component A is less than 500, then it will be difficult toobtain adequate mechanical strength (rubber hardness and elongation) andso forth when this curable composition is cured. On the other hand, ifthe number average molecular weight Mn of the oxyalkylene-based polymerof component A is too high, the molecular weight per alkenyl groupincluded in each molecule will be too high, or reactivity will sufferdue to steric hindrance, so curing will usually be insufficient, andfurthermore the viscoelasticity will be too high, which tends to resultin poor workability.

There are no particular restrictions on the alkenyl groups of theabove-mentioned oxyalkylene-based polymer, but those expressed by thefollowing General Formula 1 are preferred in terms of curability.H₂C═C(R¹)—(1)

(In the formula, R¹ is a hydrogen atom or methyl group.)

One of the advantages of this curable composition is that it is easy toachieve low hardness in the cured product, and for this to be fullyrealized, it is preferable for there to be at least two alkenyl groupsat the molecule ends. Still, if there are too many alkenyl groups withrespect to the molecular weight of component A, the product will bestiff, and it will be difficult to obtain good rubber elasticity.

If component A is a polymer in which the main repeating units that makeup the main chain consist of saturated hydrocarbon-based units, this isfavorable because the cured product will have low moisture absorption,and there will be little fluctuation in electrical resistance indifferent environments. This polymer, just as with the above-mentionedoxyalkylene-based polymer, cures through a hydrosilylation reaction withcomponent B, and has at least one alkenyl group in its molecule, andtherefore becomes macromolecular and cures when the hydrosilylationreaction occurs. The number of alkenyl groups included in the moleculesof the saturated hydrocarbon-based polymer of component A must be atleast one from the standpoint of the hydrosilylation reaction withcomponent B, but from the standpoint of rubber elasticity, it ispreferable for two alkenyl groups to be present at the ends of themolecule in the case of a straight chain molecule, and for two or morealkenyl groups to be present at the molecular ends in the case of abranched molecule.

Typical examples of a polymer in which the main repeating units thatmake up the main chain are saturated hydrocarbon units includeisobutylene-based polymers, hydrogenated isobutylene-based polymers, andhydrogenated butadiene-based polymers. These polymers may includerepeating units of other components, such as in a copolymer, but it isimportant that at least 50%, and preferably at least 70%, and even morepreferably at least 90%, of the units be saturated hydrocarbon units soas not to lose the advantage of low moisture absorption afforded by asaturated hydrocarbon-based polymer.

From the standpoint of ease of handling, the polymer of component A inwhich the main repeating units that make up the main chain are saturatedhydrocarbon units should have a number average molecular weight Mn ofabout 500 to 50,000, and preferably about 1000 to 15,000, and it is bestin terms of workability for the polymer to have good fluidity in liquidform at normal temperature.

The alkenyl groups introduced into this saturated hydrocarbon-basedpolymer are the same as with the above-mentioned oxyalkylene-basedpolymer.

Therefore, as for component A, specific favorable examples of polymersthat have at least one alkenyl group in their molecule, and in which themain repeating units that make up the main chain are saturatedhydrocarbon units, include straight-chain polyisobutylene-based polymersthat have two alkenyl groups at the molecule ends, have a number averagemolecular weight Mn of 2000 to 15,000, and have an Mw/Mn (weight averagemolecular weight)/(number average molecular weight) ratio of 1.1 to 1.2,as well as hydrogenated butadiene-based and hydrogenatedpolyisoprene-based polymers with a number average molecular weight Mn ofabout 1000 to 5000.

There are no restrictions on the compound having hydrosilyl groups thatis used as component B, as long as it contains at least twosilicon-bonded hydrogen atoms in its molecule. The term “hydrosilylgroup” here refers to a group having an Si—H bond, but in the presentinvention, when two hydrogen atoms (H) are bonded to the same siliconatom (Si), this is counted as two hydrosilyl groups. If there are toomany hydrosilyl groups in the molecule of component B, they will tend toremind in the cured product, where they will cause voids and cracks, sothe molecule of component B should include no more than 50 hydrosilylgroups. From the standpoints of storage stability and controlling therubber elasticity of the cured product, the number of hydrosilyl groupsin the molecules of component B should be from 2 to 40, and preferablyfrom 2 to 30, and from the standpoint of easily preventing foamingduring curing, there should be no more than 30, and preferably three interms of making it less likely that incomplete curing will result fromdeactivation of the hydrosilyl groups. The optimal range is from 3 to30. Curability will be better if the hydrogens are each bonded to adifferent silicon, and this is also desirable in terms of the rubberelasticity of the cured product.

The number average molecular weight Mn of component B should be nohigher than 30,000 from the standpoints of roller workability,dispersibility when the conductivity imparter (component D; discussedbelow) is added, and so forth, with 20,000 or lower being preferable,and 15,000 or lower being particularly good. When reactivity andmiscibility with component A are taken into account, the number averagemolecular weight Mn of component B should be 300 to 10,000.

A specific favorable example of component B is apolyorganohydrogensiloxane. “Polyorganohydrogensiloxane” as used hererefers to a siloxane compound having a hydrocarbon group or hydrogenatom on a silicon atom. This can be either linear or cyclic. As to thespecific structure thereof, chain-form and cyclic compounds areexpressed by the following General Formulas 2 to 4.

(In the formula, 2≦m+n≦50, 2 ≦m, 0 ≦n, and R is hydrocarbon in which thenumber of carbons in the main chain is 2 to 20, and may include one ormore phenyl groups.)

(In the formula, 0<m+n≦50, 0<m, 0≦n, and R is hydrocarbon in which thenumber of carbons in the main chain is 2 to 20, and may include one ormore phenyl groups.)

(In the formula, 3≦m+n≦20, 2<m≦19, 0 n<18, and R is hydrocarbon in whichthe number of carbons in the main chain is 2 to 20, and may include oneor more phenyl groups.)

Examples of compounds that have two or more of these units include thoseexpressed by the following General Formulas 5 to 7.

(In the formula, 1≦m+n≦50, 1≦m, 0 ≦n, and R is hydrocarbon in which thenumber of carbons in the main chain is 2 to 20, and may include One ormore phenyl groups. 2≦1, R² is a divalent to tetravalent organic group,and R¹ is a divalent organic group. Depending on the structure of R², R¹may not be needed.)

(In the formula, 0≦m+n≦50, 0≦m, 0≦n, and R is hydrocarbon in which thenumber of carbons in the main chain is 2 to 20, and may include one ormore phenyl groups. 2≦1, R² is a divalent to tetravalent organic group,and R¹ is a divalent organic group. Depending on the structure of R², R¹may not be needed.)

(In the formula, 3≦m+n≦50, 1≦m, 0≦n, and R is hydrocarbon in which thenumber of carbons in the main chain is 2 to 20, and may include one ormore phenyl groups. 2≦1, R² is a divalent to tetravalent organic group,and R¹ is a divalent organic group. Depending on the structure of R², R¹may not be needed.)

Component B should be one that has good miscibility with component A andwith components C and D, or has good dispersion stability in the system.In particular, when the viscosity of the entire system is low, phaseseparation may occur and curing may be incomplete if component B doesnot have enough miscibility with the above components. Regarding thiscomponent B, it is preferable for aryl groups, alkyl groups,polyoxyalkylene groups, or the like to be contained in order to improvethe miscibility with component A. A styrene-modified or alkylgroup-modified compound is preferred in terms of being readilyavailable, while an α-methylstyrene-modified compound is preferred interms of storage stability.

For the sake of rubber elasticity, the proportion in which component Aand component B are used in the curable composition should be such thatcomponent B contains 0.2 to 5.0 mol, and preferably 0.4 to 2.5 mol, ofhydrosilyl groups per mole of alkenyl groups in component A. Thehardness and shear modulus of the conductive elastic layer can becontrolled by varying the combination of the polymer of component A andthe curing agent of component B. Specifically, if a curing agentcontaining many hydrosilyl groups per molecule is used as component B,the hardness and shear modulus of the conductive elastic layer will behigh, and conversely, if one with few hydrosilyl groups per molecule isused, the hardness and shear modulus of the conductive elastic layerwill be low.

Next, there are no particular restrictions on the hydrosilylationcatalyst used as component C, as long as it can function as ahydrosilylation catalyst, but examples include platinum by itself, solidplatinum supported on alumina or another such carrier, chloroplatinicacid (including complexes of alcohols and so on), various complexes ofplatinum, and chlorides of metals such as rhodium, ruthenium, iron,aluminum, and titanium. Of these, chloroplatinic acid, platinum-olefincomplexes, and platinum-vinylsiloxane complexes are preferred for theircatalytic activity. These catalysts may be used singly, or two or moremay be used together.

The amount in which component C is used should be 10⁻¹ to 10⁻⁸ mol, andpreferably 10⁻¹ to 10⁻⁶ mol, and particularly 10⁻³ to 10⁻⁶ mol, per moleof alkenyl groups in component A. The reaction will not proceed ifcomponent C is used in an amount less than 10⁻⁸ mol per mole of alkenylgroups in component A. On the other hand, hydrosilylation catalysts aregenerally expensive, and are also corrosive, and furthermore theygenerate large quantities of hydrogen gas causes the cured product tofoam, so the catalyst is preferably not used in an amount over 10⁻¹ molper mole of alkenyl groups in component A.

A conductivity imparter may also be added as component D to theabove-mentioned curable composition to make it into a conductivecomposition, which is desirable for use as a developing roller, chargingroller, or transfer roller. Examples of the conductivity imparter ofcomponent D include compounds able to impart conductivity, such ascarbon black, metal fines, metal oxides, organic compounds or polymershaving quaternary ammonium salt groups, carboxylic acid groups, sulfonicacid groups, sulfuric ester groups, phosphoric ester groups, or thelike, and compounds or macromolecular compounds having conductive units,typified by ether ester amide or ether imide polymers, ethyleneoxide-epihalohydrin copolymers, methoxypolyethylene glycol acrylate, andso on, and other such antistatic agents. These conductivity impartersmay be used singly, or two or more types may be used together.

The amount in which the conductivity imparter of component D is addedshould be no more than 30 wt % with respect to the combined weight ofcomponents A to C so as not to increase the rubber hardness of the curedproduct. On the other hand, this amount should be at least 10 wt % inorder to obtain uniform resistance. The added amount should bedetermined so as to strike a good balance between the required rubberhardness and obtaining a cured product with a volumetric resistivity of10³ to 10¹⁰ Ωcm.

In addition to the above-mentioned components A to D, a storagestability enhancer may also be added to the above-mentioned curablecomposition. Any ordinary stabilizer known as a storage stabilizer forcomponent B can be used as a storage stability enhancer, and there areno particular restrictions thereon as long as the intended objective canbe achieved. More specifically, compounds containing aliphaticunsaturated bonds, organic phosphorus compounds, organic sulfurcompounds, nitrogen compounds, tin compounds, organic peroxides, and soforth can be used to advantage. Specific examples include2-benzothiazolyl sulfide, benzothiazole, thiazole, dimethylacetylenedicarboxylate, diethylacetylene dicarboxylate, butylhydroxytoluene,butylhydroxyanisole, vitamin E, 2-(4-morphodinyldithio)benzothiazole,3-methyl-1-buten-3-ol, acetylenic unsaturated group-containingorganosiloxanes, ethylenic unsaturated group-containing organosiloxanes,3-methyl-1-butyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol,1-ethynyl-1-cyclohexanol, diallyl fumarate, diallyl maleate, diethylfumarate, diethyl maleate, dimethyl maleate, 2-pentenenitrile, and2,3-dicyclopropene, although this list is not meant to be comprehensive.The above-mentioned storage stability enhancers may be used singly, ortwo or more types may be used together.

Fillers, storage stabilizers, plasticizers, UV absorbents, lubricants,pigments, and so on may also be added to the above-mentioned curablecomposition in order to improve workability or lower the cost.

The conductive elastic layer can be obtained by forming a rubber layeraround the above-mentioned conductive shaft by introducing theabove-mentioned curable composition, urethane rubber, silicone rubber,or another such elastic material by casting, injection molding,extrusion molding, or the like into a mold in the center of which aconductive shaft made of SUS, an aluminum alloy, or the like has beeninstalled, and then heating and curing the material for a suitable timeat a suitable temperature. In this case, the rubber layer formed aroundthe conductive shaft may first be semi-cured and then post-cured.

The roller pertaining to the present invention is obtained by coatingthe above-mentioned conductive elastic layer with a resin that makes upthe surface layer, in a specific thickness, by dipping, spraying, rollcoating, brush coating, or another such method, and then drying andcuring this coating at a specific temperature.

The structure of the above-mentioned surface layer in the rollerpertaining to the present invention will now be described. This surfaceresin layer should have an elongation of at least 300%, and preferablyat least 400%, and the improvement in the density unevenness of thetoner image will be particularly pronounced if the elongation is between400% and 600%. If the elongation of this surface resin layer is over600%, though, toner filming will tend to occur because of the greatertackiness of the resin layer, and the components contained in the resinlayer will tend to bleed out and soil the photosensitive element andother surrounding members. From the standpoint of suppressing thetackiness of the toner, a thermoplastic elastomer or thermosettingelastomer is preferred as the material for the surface layer. A urethaneresin, fluororesin, acrylic resin, silicone resin, or the like can beused as the main component of the surface layer of theelectrophotography roller. In the case of a developing roller, afluororesin is particularly favorable from the standpoints of wearresistance, moisture absorption, and friction charging because the toneris negatively charged.

The urethane resin can be a polycarbonate urethane, polyether urethane,polyester urethane, and so on. Not only are urethane resins readilyavailable, but when they are diluted with a solvent, they can be easilyapplied over the conductive elastic layer by dipping, spraying, rollcoating, and so forth. Aqueous dispersions of these are also readilyavailable.

A polycarbonate urethane is a compound obtained by reacting apolycarbonate polyol with a polyisocyanate. A polycarbonate polyol is aknown material obtained by condensing a polyhydric alcohol withphosgene, a chloroformic ester, a dialkyl carbonate, or diallylcarbonate. 1,6-hexanediol, 1,4-butanediol, 1,3-butanediol,1,5-pentanediol, and so forth are used as the polyhydric alcohol in afavorable polycarbonate polyol, and the number average molecular weightMn thereof is preferably about 300 to 15,000. If the diol component is apolyether polyol, the product will be a polyether urethane, and if it isa polyester polyol, a polyester urethane will result. These urethanematerials may be used singly or in combinations.

A known polyisocyanate can be reacted with the various urethane rawmaterial polyols, such as tolylene diisocyanate (TDI),4,4′-diphenylmethane diisocyanate (MDI), xylene diisocyanate (XDI),hexamethylene diisocyanate (HDI), hydrogenated TDI, hydrogenated MDI,and isophorone diisocyanate (IPDI). Hydrogenated MDI and IPDI arepreferable in their balance between ready availability and low cost.

This polyurethane can be manufactured by reacting the urethane rawmaterials (a polyol and a polyisocyanate) in the presence or absence ofa suitable solvent, using a chain extender as needed. Any known chainextender can be used for this purpose, such as an aliphatic polyamine oran aromatic polyamine. Various urethane materials modified with siliconecan also be used. When used for the surface layer, the polyurethaneshould be used along with a blocked isocyanate or other suchcrosslinking agent.

A soft fluororesin is preferable as the fluororesin. Examples includeternary copolymers of tetrafluoroethylene, hexafluoropropylene, andvinylidene fluoride, and fluororubbers.

The acrylic resin can be an acrylic rubber, urethane-modified acrylicresin, silicone-modified acrylic resin, or the like.

The silicone resin can be a condensed or adduct type of dimethylsiliconeresin or the like.

The electrophotography roller pertaining to the present invention wasdescribed above primarily using a developing roller as an example, butthe roller of the present invention is not limited to a developingroller, and can also be applied to charging rollers, transfer rollers,and so forth.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of an electrophotographicdevice; and

FIG. 2 is a diagram schematically illustrating a developing roller,which is an example of the electrophotography roller pertaining to thepresent invention, and its surrounding structure.

BEST MODE FOR CARRYING OUT THE INVENTION

Examples 1 to 5 and Comparative Examples 1 and 2, which are specificexamples of a developing roller, will now be described in detail asembodiments of the electrophotography roller pertaining to the presentinvention, after which the differences between the examples and thecomparative examples will be discussed.

The developing rollers in Examples 1 to 5 and Comparative Examples 1 and2 are configured such that a conductive elastic layer is provided aroundan SUS shaft with a diameter of 10 mm, and the outer peripheral surfaceof this conductive elastic layer is covered with a surface layer. Thespecific structures of the conductive elastic layer and surface layerwill be discussed below.

One of the elastic layers 1 to 7 is used as the conductive elasticlayer.

Elastic Layer 1

100 weight parts of (A-1) an allyl-terminated oxypropylene polymer(allyl group content: 0.233 mmol/g) with a number average molecularweight Mn of 8500 and a molecular weight distribution of 2 was mixedwith (B-1) 5 weight parts of a polysiloxane-based curing agent 1 (SiHcontent: 3.9 mmol/g) expressed by the following Formula 8,

(C-1) 0.06 weight part of a 10% isopropyl alcohol solution ofchloroplatinic acid, (D-1) 10 weight parts carbon black 3030B (made byMitsubishi Chemical), and 0.04 weight part dimethyl maleate (used as acuring retarder). This mixture was defoamed under reduced pressure (120minutes at 10 mmHg), and the composition thus obtained was used to coverthe above-mentioned shaft. This product was cured by being left for 30minutes in a 140° C. mold, which produced an elastic layer 1 with athickness of approximately 5 mm. Also, the same composition as above waspacked into an aluminum mold frame that had a thickness of 5 mm and hadbeen lined with a Teflon sheet, after which this mold frame wassandwiched between the hot plates of a pressing machine, and hot pressmolding was performed for 30 minutes at 140° C., which yielded anevaluational cured sheet with a thickness of 5 mm. The JIS A hardness ofthis elastic layer 1 sheet (as measured according to the method of JIS K6301 A) was 11°, and the shear modulus (measured as viscoelasticity at0.1 Hz) was 4.8×10⁵ Pa.Elastic Layer 2

100 weight parts of (A-1) an allyl-terminated oxypropylene polymer(allyl group content: 0.233 mmol/g) with a number average molecularweight Mn of 8500 and a molecular weight distribution of 2 was mixedwith (B-2) 3.0 weight parts of a polysiloxane-based curing agent 2 (SiHcontent: 7.9 mmol/g) expressed by the following Formula 9,

(C-1) 0.06 weight part of a 10% isopropyl alcohol solution ofchloroplatinic acid, (D-1) 10 weight parts carbon black 3030B (made byMitsubishi Chemical), and 0.04 weight part dimethyl maleate (used as acuring retarder). This mixture was defoamed under reduced pressure (120minutes at 10 mmHg), and the composition thus obtained was used to coverthe above-mentioned shaft. This product was cured by being left for 30minutes in a 140° C. mold, which produced an elastic layer 2 with athickness of approximately 5 mm. Also, the same composition as above waspacked into an aluminum mold frame that had a thickness of 5 mm and hadbeen lined with a Teflon sheet, after which this mold frame wassandwiched between the hot plates of a pressing machine, and hot pressmolding was performed for 30 minutes at 140° C., which yielded anevaluational cured sheet with a thickness of 5 mm. The JIS A hardnessand shear modulus of this elastic layer 2 sheet are given in Table 1.Elastic Layer 3

100 weight parts of (A-1) an allyl-terminated oxypropylene polymer(allyl group content: 0.233 mmol/g) with a number average molecularweight Mn of 8500 and a molecular weight distribution of 2 was mixedwith (B-3) 2.8 weight parts of a polysiloxane-based curing agent 3 (SiHcontent: 9.2 mmol/g) expressed by the following Formula 10,

(C-2) 65 μL of a bis(1,3-divinyl-1,1,3,3-tetramethyldisiloxane) platinumcomplex catalyst (17.9×10⁻⁵ mmol/μL, xylene solution), (D-1) 10 weightparts carbon black 3030B (made by Mitsubishi Chemical), and 0.04 weightpart dimethyl maleate (used as a curing retarder). This mixture wasdefoamed under reduced pressure (120 minutes at 10 mmHg), and thecomposition thus obtained was used to cover the above-mentioned shaft.This product was cured by being left for 30 minutes in a 140° C. mold,which produced an elastic layer 3 with a thickness of approximately 5mm. Also, the same composition as above was packed into an aluminum moldframe that had a thickness of 5 mm and had been lined with a Teflonsheet, after which this mold frame was sandwiched between the hot platesof a pressing machine, and hot press molding was performed for 30minutes at 140° C., which yielded an evaluational cured sheet with athickness of 5 mm. The JIS A hardness and shear modulus of this elasticlayer 3 sheet are given in Table 1.Elastic Layer 4

100 weight parts of (A-1) an allyl-terminated oxypropylene polymer(allyl group content: 0.233 mmol/g) with a number average molecularweight Mn of 8500 and a molecular weight distribution of 2 was mixedwith (B-4) 3.4 weight parts of a polysiloxane-based curing agent 4 (SiHcontent: 7.6 mmol/g) expressed by the following Formula 11,

(C-2) 65 μL of a bis(1,3-divinyl-1,1,3,3-tetramethyldisiloxane) platinumcomplex catalyst (17.9×10⁻⁵ mmol/μL, xylene solution), (D-1) 10 weightparts carbon black 3030B (made by Mitsubishi Chemical), and 0.04 weightpart dimethyl maleate (used as a curing retarder). This mixture wasdefoamed under reduced pressure (120 minutes at 10 mmHg), and thecomposition thus obtained was used to cover the above-mentioned shaft.This product was cured by being left for 30 minutes in a 140° C. mold,which produced an elastic layer 4 with a thickness of approximately 5mm. Also, the same composition as above was packed into an aluminum moldframe that had a thickness of 5 mm and had been lined with a Teflonsheet, after which this mold frame was sandwiched between the hot platesof a pressing machine, and hot press molding was performed for 30minutes at 140° C., which yielded an evaluational cured sheet with athickness of 5 mm. The JIS A hardness and shear modulus of this elasticlayer 4 sheet are given in Table 1.Elastic Layer 5

100 weight parts of (A-2) an allyl-terminated polyisobutylene polymer(allyl group content: 0.20 mmol/g) with a number average molecularweight Mn of 10,000 and a molecular weight distribution of 1.2 was mixedwith 50 weight parts of a saturated hydrocarbon-based process oil (usedas a plasticizer; PW-380 made by Idemitsu Kosan), (B-3) 4.4 weight partsof the polysiloxane-based curing agent 3 (SiH content: 9.2 mmol/g)expressed by the above Formula 10, (C-2) 56 μL of abis(1,3-divinyl-1,1,3,3-tetramethyldisiloxane) platinum complex catalyst(17.9×10⁻⁵ mmol/μL, xylene solution), (D-2) 10 weight parts carbon black(#35G made by Asahi Carbon), and 0.25 weight part1-ethynyl-1-cyclohexanol (used as a curing retarder). This mixture wasdefoamed under reduced pressure (120 minutes at 10 mmHg), and thecomposition thus obtained was used to cover the above-mentioned shaft.This product was cured by being left for 30 minutes in a 150° C. mold,which produced an elastic layer 5 with a thickness of approximately 5mm. Also, the same composition as above was packed into an aluminum moldframe that had a thickness of 5 mm and had been lined with a Teflonsheet, after which this mold frame was sandwiched between the hot platesof a pressing machine, and hot press molding was performed for 30minutes at 150° C., which yielded an evaluational cured sheet with athickness of 5 mm. The JIS A hardness and shear modulus of this elasticlayer 5 sheet are given in Table 1.

Elastic Layer 6

100 weight parts of (A-1) an allyl-terminated oxypropylene polymer(allyl group content: 0.233 mmol/g) with a number average molecularweight Mn of 8500 and a molecular weight distribution of 2 was mixedwith (B-5) 9.5 weight parts of a polysiloxane-based curing agent 5 (SiHcontent: 2.7 mmol/g) expressed by the following Formula 12,

(C-1) 0.06 weight part of a 10% isopropyl alcohol solution ofchloroplatinic acid, (D-1) 10 weight parts carbon black 3030B (made byMitsubishi Chemical), and 0.04 weight part dimethyl maleate (used as acuring retarder). This mixture was defoamed under reduced pressure (120minutes at 10 mmHg), and the composition thus obtained was used to coverthe above-mentioned shaft. This product was cured by being left for 30minutes in a 140° C. mold, which produced an elastic layer 6 with athickness of approximately 5 mm. Also, the same composition as above waspacked into an aluminum mold frame that had a thickness of 5 mm and hadbeen lined with a Teflon sheet, after which this mold frame wassandwiched between the hot plates of a pressing machine, and hot pressmolding was performed for 30 minutes at 140° C., which yielded anevaluational cured sheet with a thickness of 5 mm. The JIS A hardnessand shear modulus of this elastic layer 6 sheet are given in Table 1.Elastic layer 7

100 weight parts of (A-1) an allyl-terminated oxypropylene polymer(allyl group content: 0.233 mmol/g) with a number average molecularweight Mn of 8500 and a molecular weight distribution of 2 was mixedwith (B-1) 4.2 weight parts of the polysiloxane-based curing agent 1(SiH content: 3.9 mmol/g) expressed by the above Formula 8, (C-1) 0.06weight part of a 10% isopropyl alcohol solution of chloroplatinic acid,(D-1) 10 weight parts carbon black 3030B (made by Mitsubishi Chemical),and 0.04 weight part dimethyl maleate (used as a curing retarder). Thismixture was defoamed under reduced pressure (120 minutes at 10 mmHg),and the composition thus obtained was used to cover the above-mentionedshaft. This product was cured by being left for 30 minutes in a 140° C.mold, which produced an elastic layer 7 with a thickness ofapproximately 5 mm. Also, the same composition as above was packed intoan aluminum mold frame that had a thickness of 5 mm and had been linedwith a Teflon sheet, after which this mold frame was sandwiched betweenthe hot plates of a pressing machine, and hot press molding wasperformed for 30 minutes at 140° C., which yielded an evaluational curedsheet with a thickness of 5 mm. The JIS A hardness and shear modulus ofthis elastic layer 7 sheet are given in Table 1.

Next, the surface layer 1 discussed below was used for the surface layerthat covered the outer periphery of the conductive elastic layer.

Surface Layer 1

E-980 (a polycarbonate urethane made by Nippon Miractran) was diluted to6% with a 1:1 mixed solvent of MEK (methyl ethyl ketone) and DMF(N,N-dimethylformamide), and the surface layer solution thus obtainedwas used to coat the outside of a conductive elastic layer. This coatingwas dried for 1 hour at 80° C. and 30 minutes at 140° C., which formedthe surface layer 1. A release film was coated with the resin materialthat makes up this surface layer 1, and the elongation at break wasmeasured by the method set forth in JIS K 6251 and found to be 510%. Inthis case, the surface layer was applied by dip coating to both theroller and the film, and the coating thickness was approximately 20 μm.

As shown in Table 1, developing rollers and elastic layer sheets wereproduced by combining the elastic layers 1 to 7 with the surface layer 1(represented by Examples 1 to 5 and Comparative Examples 1 and 2). TheJIS A hardness and shear modulus of the elastic layers in these exampleswere selected in order to clearly show the difference from thecomparative examples, but the present invention is not limited to thesehardness and modulus values.

TABLE 1 Elastic layer sheet Surface layer- Elastic Surface JIS A Shearmodulus attached sheet layer layer hardness (Pa) Distortion (μm) Ex. 1elastic surface 11 4.80E + 05 9 layer 1 layer 1 Ex. 2 elastic surface 155.90E + 05 8 layer 2 layer 1 Ex. 3 elastic surface 24 7.60E + 05 5 layer3 layer 1 Ex. 4 elastic surface 21 7.30E + 05 6 layer 4 layer 1 Ex. 5elastic surface 19 6.50E + 05 7 layer 5 layer 1 C.E. 1 elastic surface 83.90E + 05 15 layer 6 layer 1 C.E. 2 elastic surface 7 3.80E + 05 17layer 7 layer 1

The JIS A hardness of the elastic layer sheets shown in Table 1 wasmeasured by the method set forth in JIS K 6301 A.

The shear modulus of the elastic layer sheets shown in Table 1 was foundas follows. The frequency characteristics from 0.01 Hz to 100 Hz weremeasured for the elastic modulus in shear mode at 20° C. and 60% RHusing a viscoelasticity measurement apparatus (DMS110 made by SeikoInstrument), and the 0.1 Hz shear modulus was found. The measurementtest piece was an elastic layer sample with a thickness of 5 mm and cutto a length of 10 mm and a width of 10 mm from the cured sheet with athickness of 5 mm produced for evaluational purposes. The measurementtest piece can also be a test piece with a thickness of at least 2 mmand cut to a length of 10 mm and a width of 10 mm from the elastic layerof a roller.

The amount of distortion (μm) in the surface layer-attached sheet inTable 1 was measured as follows. A measurement sheet was separatelyproduced by using a surface layer resin material to coat a cured sheetproduced in the same manner as the evaluational sheet of theabove-mentioned elastic layer, an SUS disk-shaped jig with a thicknessof 10 mm and an outside diameter of 100 mm, and having a circularprotrusion (0.5 mm) with a width of 1 mm and an outside diameter of 30mm in its center, was placed so that this protrusion was in contact withthe surface layer of the measurement sheet, a weight of approximately 3kg was applied from above, and this was left for 24 hours with theabove-mentioned circular protrusion pushed into the sheet, after whichthe weight and the disk jig were removed, and the amount of distortionin the compressed portion after 24 hours was measured.

As is clear from Table 1, the amount of distortion after 24 hours wasless than 10 μm in Examples 1 to 5, whereas this amount was 15 μm orhigher in Comparative Examples 1 and 2, in which the shear modulus ofthe elastic layer was less than 4.0E+05 Pa (4.0×10⁵ Pa).

The developing rollers of these examples and comparative examples wereeach installed in a developing apparatus of the same construction, thedeveloping apparatus was installed in a printer, and a printing test wasconducted. The amount of penetration into the roller by thephotosensitive element was set to approximately 200 μm, and the rollerwas left in this state for 2 weeks in a normal environment of 20° C. and60% RH, after which the power to the printer was turned on and aprinting test was immediately carried out. A sharp image with no streakydensity unevenness was obtained immediately after the printer was turnedon in Examples 1 to 5, but in Comparative Examples 1 and 2, streakydensity unevenness believed to be caused by distortion of thephotosensitive element was seen immediately after the printer was turnedon, and faint density unevenness still remained 24 hours later.

INDUSTRIAL APPLICABILITY

As discussed above, when a developing roller is used that has aconductive elastic layer having a JIS A hardness of 30° or less andhaving a shear modulus of at least 4×10⁵ Pa (measured as theviscoelasticity at 0.1 Hz at 20° C. and 60% RH), the proper contactwidth in the peripheral direction can be ensured between the roller andthe photosensitive element even at a low pressing force, and there willbe little residual compression strain in the roller even when it hasbeen compressed and fixed in a state of being pressed against thephotosensitive element for an extended period. Also, a sharp toner imagewith no streaky density unevenness attributable to residual strain inthe developing roller can be obtained immediately after the compressionand fixing are released.

When the roller of the present invention is used as a charging roller,it is possible to supply a charge more uniformly to a photosensitiveelement because there is so little residual strain, and when the rollerof the present invention is used as a transfer roller, it is possible toobtain a sharp transferred image on an intermediate rotating element orrecording paper.

1. An electrophotography roller, in which a conductive shaft is disposedalong a center axis, a conductive elastic layer is providedconcentrically around said conductive shaft, and a surface layer isformed concentrically over said conductive elastic layer: wherein theconductive elastic layer comprises a reaction product of a curablecomposition whose main components are (A) a polymer that contains atleast one alkenyl group in its molecule, and in which the repeatingunits that make up the main chain consist mainly of oxyalkylene units,(B) a curing agent that contains at least two hydrosilyl groups in itsmolecule, represented by the following general chemical formula

where 2≦m+n≦50, 2≦m, and 1≦n, (C) a hydrosilylation catalyst, and (D) aconductivity imparter; wherein the conductive elastic layer has a JIS Ahardness of 30° or less, and the shear modulus of the conductive elasticlayer, measured as the viscoelasticity at 0.1 Hz in an environment of20° C. and 60% RH, is at least 4×10⁵ Pa; and wherein the main componentof the surface layer is either a single resin selected from the groupconsisting of urethane resins, acrylic resins, silicone resins, andfluororesins, or a blend of these resins, and material of the surfacelayer has an elongation between 300% and 600%.
 2. The electrophotographydevelopment roller according to claim 1, wherein material of the surfacelayer has an elongation between 400% and 600%.
 3. The electrophotographydevelopment roller according to claims 1 or 2, wherein the surface layeris made of urethane resins.